The field of this invention is marine risers for offshore oil well drilling operations or the like.
In offshore oil well drilling operations, it is necessary to extend a casing from a floating drilling platform or vessel to the subsea wellhead. Such casing is generally known as a "marine riser". Marine riser systems generally consist of a series of hollow pipe sections which are connected both to the wellhead and to the floating platform. Examples of marine riser systems are found in U.S. Pat. Nos. 3,465,817 and 3,502,143.
Marine risers are subjected to severe environmental forces including the effects of wind, waves and current as well as hydrostatic pressure. In addition, the weight of a column of riser pipe sections of steel plus the weight of drilling fluid circulated through the riser sections tend to exert critical compression loading on a riser column. This compression column loading is generally compensated for by riser tensioners which are known in the art. However, several U.S. patents are generally directed to the use of various devices to render riser pipe sections buoyant in order to reduce or eliminate the need for riser tensioners. See, for example, U.S. Pat. Nos. 3,768,842; 3,017,934 and 3,221,817.